Methods for operating a furnace

ABSTRACT

A method for operating a furnace, such as, for example, a fluidized bed reactor, includes introducing an alkali-containing material and a hydrous clay into the furnace, the hydrous clay having a moisture content of at least about 5% by weight. The method further includes heating at least a portion of the alkali-containing material and hydrous clay, such that at least a portion of the hydrous clay is at least partially calcined and the at least partially calcined clay adsorbs at least a portion of alkali present in the furnace. The method further includes removing at least a portion of the at least partially calcined clay and adsorbed alkali from the furnace.

RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Application No. 61/108,700, filed on Oct. 27, 2008,and the benefit of priority of U.S. application Ser. No. 12/263,705,filed on Nov. 3, 2008, the disclosures of both of which are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to methods for operating furnaces, andmore particularly, to methods for operating furnaces such as, forexample, fluidized-bed reactors, by including introduction of hydrousclay into the furnace.

BACKGROUND

Combustion processes may be used in power plant furnaces to generateheat for operating a boiler or steam generator, which generates electricpower. The fuel used for such processes may include coal, petroleumcoke, and/or biofuel derived from biomass. The fuel may include analkali-containing material. Other alkali-containing materials known tothose skilled in the art may be used in the processes to, for example,capture environmental pollutants.

Some power plants may include systems that operate using, for example, aprocess sometimes referred to as a “fluidized-bed combustion” process.One example of such a process is a circulating fluidized-bed combustionprocess, which may be used for electric power generation. Some examplesof circulating fluidized-bed reactors may include gasifiers, combustors,and steam generators, and typically, circulating fluidized-bed reactorshave an upright furnace or boiler.

During operation, fuel, for example, particulate fuel, is introducedinto a lower part of a furnace, and primary and secondary gases, forexample, air, may be supplied through a bottom and/or sidewalls of thefurnace. Combustion of the fuel takes place in a bed of fuel particlesand other solid particles, such as, for example, calcium carbonate,which may be included for sulfur dioxide capture, and/or inert material.For example, the fluidized-bed reactor (i.e., furnace) may be configuredto suspend the bed of fuel particles and other materials onupward-blowing jets of the primary and/or secondary gases during thecombustion process. The upward-blowing jets facilitate mixing of thefluid particles and other materials, which serves to improve combustionby, for example, reducing undesirable emissions and increasingcombustion and heat transfer efficiency.

Exhaust gas and/or solid particles entrained in the bed may leave thefurnace via an exhaust port in, for example, an upper part of thefurnace and may be passed to a particle separator. In the particleseparator, most or substantially all of the solid particles may beseparated from the exhaust gas. Typically, one or more cyclones, whichuse tangential forces to separate particles from exhaust gas, arecoupled with the furnace. During normal operation, cyclones may becapable of separating about 99.9% of the particles from the exhaust gas.

The exhaust gas and any remaining solid particles, or fly ash, may thenbe passed through additional processing units before ultimately beingreleased into the atmosphere. For example, in an atmospheric circulatingfluidized-bed system, the exhaust gas flows through a boiler and pastits boiler tubes containing a supply of water, providing heat to convertthe water to steam. The steam may then be used to drive a steam turbine,generating electricity. The exhaust gas may be passed through a heatexchanger to recover at least a portion of the heat generated during thecombustion process, and the exhaust gas may be passed throughenvironmental processing units to reduce levels of undesirableemissions, such as pollutants, for example, nitrogen oxides (“NOx”),sulfur oxides (“SOx”), and/or particulate matter (“PM”).

Solid particles recovered in the particle separator, such as bottom ash,may be returned to the bed in the circulating fluidized-bed reactor forsubsequent reaction and/or removal from the bed. Energy bound in theheated bottom ash may be at least partially recovered, for example, inan integrated fluidized-bed heat exchanger, before the ash is recycledto the circulating fluidized-bed reactor.

An exemplary integrated fluidized-bed heat exchanger is an INTREX™ steamsuperheater (Foster Wheeler Ltd.; Clinton, N.J., USA). In such a heatexchanger, bottom ash separated in a cyclone may pass over the INTREX™steam superheater before returning to the circulating fluidized-bedreactor. The use of other fluidized-bed heat exchangers known to thoseskilled in the art is contemplated.

Combustion of the fuel particles and/or heating of other materials(e.g., calcium carbonate) may result in heating of alkali-containingmaterials, such that alkali compounds contained therein are released.The released alkali compounds may react with ash or other inorganiccomponents, such as, for example, sulfur, chlorine, and/or silicon,which may result in undesirable deposits, ash accumulation, and/orcorrosion occurring on exposed surface areas of the fluidized-bedcomponents, for example, on furnace walls and/or boiler tubes. Suchdeposits and corrosion may lead to less efficient operation and/or lostproduction due to increased maintenance-related down time. Without beinglimited by theory, the alkali compounds may be released in a liquid orvapor form, which may be entrained in the fluidized bed or with theparticles making up the fluidized bed. The alkali compounds may causeash particles to stick together, leading to an undesirable ashaccumulation (e.g., on boiler tubes) and fouling of the reactor systemsurfaces. Without being limited by theory, the alkali components andsiliceous component of the ash may form a eutectic mixture that formcrystalline/amorphous deposits on the reactor surfaces.

As a result, it may be desirable to remove at least a portion of thealkali compounds from the furnace before they react with the ash and/orother inorganic components, for example, to reduce or preventundesirable deposits and/or corrosion.

Davidsson et al., in an article entitled, “Kaolin Addition duringBiomass Combustion in a 35 MW Circulating Fluidized Bed-Boiler”, Energy& Fuels 2007, 21, 1959-1966, describe adding kaolin to a circulatingfluidized-bed boiler. Davidsson et al. specify using kaolin sold under aproduct name Intrafil C® and obtained from Imerys Minerals Ltd., andstate that the addition of this highly-processed kaolin results inremoval of alkali from the furnace. In particular, the kaolin used byDavidsson et al. is highly processed and may have a very low moistureand/or iron content.

Although the kaolin added by Davidsson et al. to the circulatingfluidized-bed boiler may result in the removal of alkali from thefurnace, the method described by Davidsson et al. may suffer from anumber of possible drawbacks. For example, the kaolin added is a highlyprocessed, fine powder kaolin, and an undesirably large portion of thekaolin was carried out of the circulating fluidized-bed reactor by theflue gases, and thus only a relatively small fraction of the kaolinremained in the furnace. This may result from, for example, the finenessof the kaolin, 36% of the kaolin having a particle size distribution ofless than 1 μm, and 55% having a particle size distribution of less than2 μm. Davidsson et al. indicate that an undesirably high amount of thekaolin ended up in the fly ash. Moreover, the kaolin used by Davidssonet al. may not be sufficiently cost effective due to the costs sometimesassociated with such highly processed kaolin.

In light of these possible drawbacks, it may be desirable to identify aless costly method for removing alkali from a furnace, for example, thefurnace of a fluidized-bed reactor.

SUMMARY

In the following description, certain aspects and embodiments willbecome evident. It should be understood that the aspects andembodiments, in their broadest sense, could be practiced without havingone or more features of these aspects and embodiments. It should beunderstood that these aspects and embodiments are merely exemplary.

One aspect of the disclosure relates to a method for combusting fuel inthe presence of an alkali-containing material. The method may includeintroducing fuel, calcium carbonate, and hydrous clay into a furnaceconfigured to combust the fuel, wherein the hydrous clay has a moisturecontent of at least about 5% by weight. The method further includescombusting at least a portion of the fuel, such that the hydrous clay isat least partially calcined and the at least partially calcined clayadsorbs at least a portion of alkali present in the furnace.

Another aspect of the disclosure relates to a method for operating afluidized-bed reactor. The method includes introducing analkali-containing material and hydrous clay into the fluidized-bedreactor. As used herein, “alkali-containing materials” and “alkalicompounds” refer to materials containing carbonates and/or hydroxides ofan alkali metal and/or alkaline earth metal, and/or salts and/or ions ofan alkali metal and/or alkaline earth metal. The hydrous clay has amoisture content of at least about 5% by weight. The method furtherincludes heating at least a portion of the alkali-containing materialand hydrous clay, such that at least a portion of the hydrous clay is atleast partially calcined and the calcined clay adsorbs at least aportion of alkali present in the fluidized-bed reactor. The methodfurther includes removing at least a portion of the at least partiallycalcined clay and adsorbed alkali from the fluidized-bed reactor.

According to yet another aspect, a method for reducing alkali ashaccumulation in a fluidized-bed reactor includes introducing analkali-containing material into the fluidized-bed reactor andintroducing hydrous clay into the fluidized-bed reactor, wherein thehydrous clay has a moisture content of at least about 5% by weight. Themethod further includes heating the alkali-containing material and thehydrous clay, such that at least a portion of the hydrous clay is atleast partially calcined and the at least partially calcined clayadsorbs at least a portion of alkali present in the fluidized-bedreactor. The method further includes removing at least a portion of thecalcined clay and adsorbed alkali from the fluidized-bed reactor.

In still a further aspect, a method for operating a fluidized-bedreactor includes introducing hydrous clay, fluidization media, and fuelinto a furnace for combusting the fuel, such that a fluidized-bed isprovided therein. At least a portion of the fluidized bed includes ashparticles associated with alkali compounds. An amount of the hydrousclay ranging from about 30% to about 50% has a particle size of lessthan about 1 μm. The method further includes heating at least a portionof the fuel and hydrous clay, such that at least a portion of thehydrous clay is at least partially calcined. The method also includesreacting the alkali compounds with at least a portion of the at leastpartially calcined clay, wherein the at least partially calcined claycomprises solid material particles having a plurality of adsorptionsites for adsorbing at least a portion of the alkali compounds.

Aside from the structural and procedural arrangements set forth above,the embodiments could include a number of other arrangements, such asthose explained hereinafter. It is to be understood that both theforegoing description and the following description are exemplary only.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to a number of exemplaryembodiments. Fuel may by combusted in a furnace to produce heat, and theheat produced may, in turn, be used to generate electric power, via, forexample, a steam generator. Heating the fuel and/or materials (e.g.,calcium carbonate) associated with a combustion process may result inrelease of alkali in the furnace. According to some embodiments, hydrousclay may be added to the furnace, and the heat may at least partiallycalcine the hydrous clay, such that the at least partially calcined clayis available to act as an adsorbent for at least a portion of the alkaliwithin the furnace.

According to some embodiments, a method of operating a circulatingfluidized-bed reactor system may include at least the steps ofintroducing an alkali-containing material into a circulatingfluidized-bed furnace (e.g., a reactor), introducing a hydrous clayhaving a moisture content of at least about 5% (e.g., a moisture contentranging from about 5% by weight to about 15% by weight) into thecirculating fluidized-bed reactor, and removing at least a portion ofthe clay (e.g., an at least partially calcined portion of the hydrousclay) from the circulating fluidized-bed reactor system.

According to some embodiments, hydrous clay may include lump clay, forexample, hydrous clay that may be partially dried to a moisture contentranging from at least about 1% by weight to at least about 50% byweight. According to some embodiments, the lump clay may be partiallydried to a moisture content ranging from about 4% by weight to about 16%by weight, for example, from about 8% by weight to about 12% by weight(e.g., about 10% by weight), from about 5% by weight to about 10% byweight, or from about 10% by weight to about 15% by weight.

In one embodiment, the lump clay may comprise hydrous clay agglomerateshaving a size of about 1 inch or less. In other embodiments, the lumpclay may comprise hydrous clay agglomerates having a size of about ¾inch or less, for example, about ½ inch or less. In other embodiments,the lump clay may comprise hydrous clay agglomerates having a size ofabout ¼ inch or less (e.g., to about ⅛ inch or less). In otherembodiments, the lump clay may comprise hydrous clay agglomerates havinga maximum lump size of not more than about 3 inches, such as not morethan about 2 inches or not more than about 1 inch. In some embodiments,the lump clay may comprise hydrous clay agglomerates having a maximumlump size ranging from about 0.25 inch to about 2 inches, such as, forexample, from about 0.25 inch to about 1 inch.

According to some exemplary embodiments, the hydrous clay may includeone or more of lump clay, clay that has been shredded and/or crushed,non-beneficiated clay, kaolinite, ball clay (e.g., clay that includesabout 20-80% kaolinite, 10%-25% mica, and/or 6%-65% quartz), and clayderived from overburden from a kaolinite mining operation (e.g., clayderived from material located over kaolinite deposits being mined).According to some embodiments, the hydrous clay may have a BET surfacearea of at least about 9 m²/g, for example, at least about 10 m²/g or atleast about 15 m²/g.

Alkali-containing materials according to some embodiments may serve asfuel for combustion. For example, alkali-containing materials mayinclude one or more of coal, petroleum coke, and biofuel (e.g., fuelobtained from biomass). Exemplary coal sources include, withoutlimitation, brown coal, lignite and bituminous coal, such as, forexample, eastern bituminous coal, coking coal, Jurassic coal, Triassiccoal, Permian coal, and carboniferous coal. In other embodiments,alkali-containing materials are substantially absent from the fuel usedfor combustion.

According to some embodiments, alkali-containing materials may includecalcium carbonate. In some embodiments, the calcium carbonate may beprovided as particulate limestone, marble, chalk, dolomite, aragoniticsand, sea shells, coral, and/or mixtures thereof. In one embodiment, thealkali-containing material may include a calcium carbonate originatingfrom a marine originating deposit, for example, wherein the alkali mayinclude residual salt from seawater.

According to some embodiments, fuel and/or alkali-containing material(s)and hydrous clay may be combined before being supplied to a furnace. Forexample, fuel and/or alkali-containing material and hydrous clay may bemixed and/or blended prior to combustion. In some embodiments, at leastone of coal and petroleum coke may be mixed and/or blended with thehydrous clay. In other embodiments, calcium carbonate may be mixedand/or blended with the hydrous clay. In yet other embodiments, thehydrous clay may be added directly to a fluidized-bed reactor system.For example, the hydrous clay may be added to the furnace or the hydrousclay may be added to the bottom ash stream that is gravity fed to thefurnace.

According to some embodiments, combustion may occur in a furnace, forexample, a furnace that is part of a fluidized-bed reactor system forgenerating electric power via, for example, a steam generator. Forexample, the furnace may be part of a circulating fluidized-bed reactorsystem. The furnace may be part of other systems for combustingalkali-containing materials known to those skilled in the art.

In some embodiments, the hydrous clay may be at least partiallyconverted to a calcined clay in the circulating fluidized-bed reactor.In some embodiments, the at least partially calcined clay may serve toadsorb at least a portion of alkali present in the fluidized-bedreactor.

Hydrous clay may be introduced, in some embodiments, at least twice tothe circulating fluidized-bed reactor. In some embodiments, at least aportion of the alkali-containing material may be blended with at least aportion of the hydrous clay before the blended alkali-containingmaterial and hydrous clay is introduced into the circulatingfluidized-bed reactor. According to some embodiments, at least a portionof the hydrous clay may be introduced into a lower portion of thecirculating fluidized-bed reactor. In some embodiments, at least aportion of the hydrous clay may be introduced into the back end of thecirculating fluidized-bed reactor. In some embodiments, at least aportion of the hydrous clay may be introduced into an upper portion ofthe circulating fluidized-bed reactor. According to some embodiments, atleast a portion of the hydrous clay may be introduced into an ash-slurryside of an integrated fluidized-bed heat exchanger.

Before alkali-containing material(s) and hydrous clay are introduced tothe furnace, the size of at least one of the alkali-containing materialand hydrous clay may, in some embodiments, be subjected to at least onephysical modification process. For example, physical modificationprocess(es) may serve to reduce the size of the at least one of thealkali-containing material and hydrous clay to, for example, about 1inch or less. In some embodiments, an exemplary physical modificationprocess may reduce the size of at least one of the alkali-containingmaterial and hydrous clay to about ¾ inch or less, for example, to about½ inch or less. In some embodiments, the exemplary physical modificationprocess may reduce the size of the at least one of the alkali-containingmaterial and hydrous clay to about ¼ inch or less (e.g., to about ⅛ inchor less). In other embodiments, the at least one of thealkali-containing material and hydrous clay may comprise hydrous clayagglomerates having a maximum lump size of not more than about 3 inches,such as not more than about 2 inches or not more than about 1 inch.Exemplary physical modification processes may include at least one ofmilling, hammering, roll crushing, drying, grinding, screening,extruding, triboelectric separating, liquid classifying, and airclassifying.

According to some embodiments, the exemplary methods may include a stepof removing a portion of the at least partially calcined clay from thefurnace. For example, a portion of the at least partially calcined claymay be removed periodically. In some embodiments, for example, at leasta portion of a fluidized bed may be removed (e.g., via pumping) once thebed reaches a predetermined height in a fluidized bed reactor. In someembodiments, at least partially calcined clay removal from thecirculating fluidized bed reactor may be substantially continuous. Insome embodiments, a portion of the at least partially calcined clay maybe removed at a point external to the fluidized-bed reactor. Forexample, at least a portion of the at least partially calcined clay maybe removed at an outlet of a particle separator of the fluidized-bedreactor system. In some embodiments, at least a portion of the at leastpartially calcined clay may be removed after passing through anintegrated fluidized-bed heat exchanger. In some embodiments, at least aportion of the at least partially calcined clay may be removed from anoverhead outlet of a cyclone, and such portion may be removed via atleast one of a fabric filter and a baghouse.

According to some embodiments, inert material may be introduced into thefurnace. Exemplary inert materials may include, for example and withoutlimitation, sand, residues of fuel, and/or gypsum. In some embodiments,a fine inert material may be selected to improve separation efficiencyin one or more cyclones that may be associated with the furnace. In someembodiments, a coarse inert material may be selected to increase thebulk of a fluidization bed.

The amount of hydrous clay introduced into the furnace may be selectedbased on, for example, an amount sufficient to maintain boilerefficiency. One measure of boiler efficiency relates to boiler steamtemperature. In some embodiments, hydrous clay may be added in an amountsufficient to maintain a boiler steam temperature ranging from about930° C. to about 1010° C., for example, in an amount sufficient tomaintain a boiler steam temperature ranging from about 950° C. to about1010° C. In some embodiments, hydrous clay may be added in an amountsufficient to maintain a boiler steam temperature ranging from about970° C. to about 1010° C., for example, in an amount sufficient tomaintain a boiler steam temperature ranging from about 1000° C. to about1010° C. For example, for some fluidized bed reactors, an amount ofhydrous clay (e.g., lump semi-dried kaolin) ranging from about 25 toabout 85 tons per day may be added, for example, an amount ranging fromabout 40 to about 50 tons per day may be added. For example, forrelatively low sulfur fuel, about 35 tons per day of hydrous clay may beadded, and for relatively high sulfur fuel, about 50 tons per day ofhydrous clay may be added. The fuel may include, for example, acombination of about 85% pet coke and about 15% coal, totaling about 100tons per hour of fuel.

The hydrous clay used in the exemplary methods disclosed herein may havea measurable moisture content. In some embodiments, the hydrous clay mayhave a moisture content of at least about 1% (e.g., at least about 5%).For example, the moisture content of the hydrous clay may range fromabout 5% by weight to about 15% by weight, for example, from about 8% byweight to about 12% by weight. In some embodiments, the hydrous clay mayhave a moisture content ranging from about 9% by weight to about 11% byweight, for example, about 10% by weight (e.g., lump clay having amoisture content of about 10%).

The hydrous clay used in the exemplary methods disclosed herein may takevarious forms and/or may have undergone various processes. For example,the hydrous clay may include shredded and/or crushed clay. In someembodiments, hydrous clay may be non-beneficiated clay. As used herein,non-beneficiated clay may include clay that has not been subjected to atleast one process chosen from dispersion, blunging, selectiveflocculation, ozone bleaching, classification, magnetic separation,chemical leaching, froth flotation, and dewatering of the clay. In someembodiments, at least a portion of the hydrous clay may be kaolinite,for example, a hydrous aluminosilicate having a formula, Al₂Si₂O₅(OH)₄.In some embodiments, the hydrous clay may include ball clay. In someembodiments, the hydrous clay may include clay derived from overburdenfrom a kaolin mining operation. In some embodiments, the hydrous claymay be clay derived from crude clay having a moisture content of atleast about 15%. For example, the hydrous clay may includemontmorillonitic kaolin.

The hydrous clay used in the exemplary methods disclosed herein may be acombination of hydrous clays. For example, at least one hydrous clay maybe selected to provide bonding strength to the combination of hydrousclays. In some embodiments, at least one hydrous clay may be selected toincrease the coarseness of the hydrous clay combination.

According to some embodiments, the hydrous clay used in the exemplarymethods disclosed herein may have a measurable BET surface area. Forexample, the BET surface area may be at least about 9 m²/g, for example,the BET surface area may be at least about 10 m²/g or at least about 15m²/g.

The hydrous clay used in the exemplary methods disclosed herein may havea measurable particle size. Particle sizes and other particle sizeproperties referred to herein, such as particle size distribution(“psd”), may be measured using a SEDIGRAPH 5100 instrument as suppliedby Micromeritics Corporation. For example, the size of a given particlemay be expressed in terms of the diameter of a sphere of equivalentdiameter that sediments through the suspension, that is, an equivalentspherical diameter or “esd.”

The measurable particle size may indicate the relative coarseness of thehydrous clay. In some embodiments, about 30% to about 50% of the hydrousclay has a particle size less than about 1 μm. In some embodiments,about 35% to about 45% of the hydrous clay has a particle size less thanabout 1 μm. In some embodiments, about 30% to about 40% of the hydrousclay has a particle size less than about 1 μm. In some embodiments,about 40% to about 50% of the hydrous clay has a particle size less thanabout 1 μm.

In some embodiments, about 60% to about 80% of the hydrous clay has aparticle size less than about 2 μm. In some embodiments, about 65% toabout 75% of the hydrous clay has a particle size less than about 2 μm.In some embodiments, about 60% to about 70% of the hydrous clay has aparticle size less than about 2 μm. In some embodiments, about 70% toabout 80% of the hydrous clay has a particle size less than about 2 μm.

The hydrous clay used in the exemplary methods disclosed herein may havea measurable washed screen residue, for example, a measurable +325washed screen retention. For example, the +325 mesh wash screenretention may be from about 0.5% to about 9%. In some embodiments, the+325 mesh wash screen retention may be from about 0.5% to about 8%. Insome embodiments, the +325 mesh wash screen retention may be from about0.5% to about 5%. In some embodiments, the +325 mesh wash screenretention may be from about 0.5% to about 1.5%. In some embodiments, the+325 mesh wash screen retention may be from about 4% to about 5%. Insome embodiments, the +325 mesh wash screen retention may be from about1% to about 4.5%. In some embodiments, the +325 mesh wash screenretention may be from about 4.5% to about 9%.

The exemplary methods disclosed herein may be used in association with avariety of fuel(s) and/or alkali-containing materials. In someembodiments, the fuel may contain an alkali material.

According to some embodiments, the fuel may include coal. Exemplary coalsources include, without limitation, lignite and bituminous coal, suchas, for example, eastern bituminous coal, coking coal, Jurassic coal,Triassic coal, Permian coal, and carboniferous coal.

According to some embodiments, the fuel associated with the exemplarymethods disclosed herein may include petroleum coke, for example, acarbonaceous solid derived from oil refinery coker and cracking units.In some embodiments, the fuel may include sand of petroleum coke. Insome embodiments, the fuel may include combinations of coal andpetroleum coke.

According to some exemplary methods disclosed herein, increasing theamount of hydrous clay added to the reactor system may permit areduction in the amount of coal combusted in the circulatingfluidized-bed reactor. For example, for about one part by weight ofhydrous clay introduced to the system, the amount of coal introduced tothe system may be reduced by about 5 parts by weight of coal.

According to some embodiments, the fuel associated with exemplarymethods disclosed herein may include biofuel derived from, for example,biomass. Exemplary biomass sources may include, without limitation, woodpellets, straw pellets, peat, lignocellulose, waste biomass, such asbagasse, wheat stalks, corn stalks, oat stalks, and/or energy biomass,such as, for example, grasses of the Miscanthus genus.

In some embodiments, alkali-containing materials may include materialsselected to reduce at least one of SOx and NOx. For example, thealkali-containing material(s) selected to reduce at least one of SOx andNOx may include calcium carbonate. For example, calcium carbonate may bederived from the sea. According to some embodiments, the material(s) mayinclude at least one of a SOx- and NOx-getter.

According to one exemplary method, a method of operating a fluidized bedreactor system for reacting fuel may include introducing solid materialparticles, fluidization medium, and fuel into a reactor system having areactor chamber to provided a fluidized bed therein. The fluidized bedmay include ash particles associated with at least one alkali compound.The exemplary method may further include reacting the at least onealkali compound with at least a portion of the solid material particles.In some embodiments, the solid material particles may have a pluralityof adsorption sites for adsorption of the at least one alkali compound.The solid material particles may include at least one hydrous clay. Theat least one hydrous clay may be heated in the reactor system such thatat least a portion of the at least one hydrous clay is at leastpartially calcined. The reacted solid material particles may be removedfrom the reactor chamber.

In some embodiments, about 30% to about 50% of the hydrous clay has aparticle size less than about 1 μm. In some embodiments, about 35% toabout 45% of the hydrous clay has a particle size less than about 1 μm.In some embodiments, about 30% to about 40% of the hydrous clay has aparticle size less than about 1 μm. In some embodiments, about 40% toabout 50% of the hydrous clay has a particle size less than about 1 μm.

In some embodiments, about 60% to about 80% of the hydrous clay has aparticle size less than about 2 μm. In some embodiments, about 65% toabout 75% of the hydrous clay has a particle size less than about 2 μm.In some embodiments, about 60% to about 70% of the hydrous clay has aparticle size less than about 2 μm. In some embodiments, about 70% toabout 80% of the hydrous clay has a particle size less than about 2 μm.Particle size measurement may be defined by, for example, standardSedigraph “psd” analytical methods, as previously defined.

In addition to the hydrous clay, in some embodiments, the solid materialparticles may include at least one of a SOx- and NOx-getter and/or aninert material. An exemplary SOx-getter may include be, for example andwithout limitation, calcium carbonate. Exemplary inert materials mayinclude, for example, sand, gypsum, and/or residues of fuel.

EXAMPLE

A circulating fluidized-bed reactor system was operated using acombination of petroleum coke and coal as fuel. A sample of hydrousclay, including a fine grained montmorillonitic kaolin clay (see Tableof exemplary characteristic data below), was blended with coal. The coalhad a moisture content ranging from about 12% to about 15% whereas thehydrous clay had a moisture content ranging from 8% to 12%. The hydrousclay and coal mixture was fed into the circulating fluidized-bed reactoralong with petroleum coke. The ratio of hydrous clay/coal to petroleumcoke was about 20% clay/coal and about 80% petroleum coke, with thehydrous clay addition rate ranging from 25 tons per day to 45 tons perday.

TABLE CHEMICAL ANALYSIS Si0₂ (%) 46.5 Al₂O₃ (%) 37.5 Fe₂O₃ (%) 1.0 TiO₂(%) 1.3 K₂O (%) 0.3 Na₂O (%) 0.1 CaO (%) 0.3 MgO (%) 0.3 L.O.I. (%) 13.2Carbon (%) 0.10 Sulfur (%) 0.13 PHYSICAL PROPERTIES pH 4.5 M.B.I.(meq/100) 10.5 Specific Surface Area 24.0 (m²/g) PARTICLE SIZE +325 Mesh(% Retained) 1.0 % <20 (μm) 99 % <10 (μm) 97 % <5 (μm) 94 % <2 (μm) 85 %<1 (μm) 76 % <0.5 (μm) 65 * Extruded 50/50 Clay/Flint

Adding the hydrous clay to the system improved at least boilerefficiency. The steam temperature exiting the boiler, which is onemeasure of boiler efficiency, did not decrease to about 900° C., whichis the expected steam temperature after a few weeks in service and farlower than the optimal 1000° C. target. Instead, the steam temperatureimproved to about 950° C. after the initial addition of the hydrousclay. Following an increase of the amount of hydrous clay fed into thesystem, the steam temperature improved further to about 970° C.

Other embodiments of the disclosure will be apparent to those skilled inthe art from consideration of the specification and practice of theexemplary embodiments disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the disclosure being indicated by the followingclaims.

1-67. (canceled)
 68. A method for combusting fuel in the presence of analkali-containing material, the method comprising: introducing fuel intoa furnace configured to combust the fuel; introducing hydrous clayhaving a moisture content of at least about 5% by weight into thefurnace; and heating at least a portion of the fuel and hydrous clay,such that at least a portion of the hydrous clay is at least partiallycalcined and the at least partially calcined clay adsorbs at least aportion of alkali present in the furnace.
 69. The method of claim 68,wherein the hydrous clay has a moisture content ranging from about 5% byweight to about 15% by weight.
 70. The method of claim 68, wherein thehydrous clay has a moisture content ranging from about 8% by weight toabout 12% by weight.
 71. The method of claim 68, wherein the hydrousclay comprises lump clay.
 72. The method of claim 68, wherein thehydrous clay comprises clay that has been at least one of shredded andcrushed.
 73. The method of claim 68, wherein the hydrous clay comprisesnon-beneficiated clay.
 74. The method of claim 68, wherein the hydrousclay comprises kaolinite.
 75. The method of claim 68, wherein thehydrous clay comprises ball clay.
 76. The method of claim 68, whereinthe hydrous clay comprises clay derived from overburden from a kaolinmining operation.
 77. The method of claim 68, wherein the hydrous clayhas a BET surface area of at least about 9 m²/g.
 78. The method of claim68, wherein the hydrous clay has a BET surface area of at least about 15m²/g.
 79. The method of claim 68, wherein hydrous clay comprises clayderived from crude clay having a moisture content of at least about 15%.80. The method of claim 68, further comprising calcium carbonate intothe furnace.
 81. The method of claim 68, further comprisingincorporating the furnace into a fluidized-bed reactor system.
 82. Themethod of claim 81, wherein the fluidized-bed reactor system is acirculating fluidized-bed reactor system.
 83. The method of claim 68,wherein the step of heating results in calcining at least a portion ofthe hydrous clay, and the method further comprises: adsorbing at least aportion of alkali in the furnace via the calcined clay; and removing atleast a portion of the calcined clay and adsorbed alkali from thefurnace.
 84. The method of claim 68, wherein the fuel is coal, petroleumcoke, or biofuel, or a combination of any of the foregoing.
 85. Themethod of claim 68, wherein the hydrous clay comprises hydrous clayagglomerates having a size of no more than about 3 inches.
 86. Themethod of claim 85, wherein the hydrous clay agglomerates have a size ofno more than about 2 inches.
 87. The method of claim 86, wherein thehydrous clay agglomerates have a size of no more than about 1 inch. 88.A method for combusting fuel in the presence of an alkali-containingmaterial, the method comprising: introducing fuel and calcium carbonateinto a furnace configured to combust the fuel; introducing hydrous clayhaving a moisture content of at least about 5% by weight into thefurnace; and heating at least a portion of the fuel, calcium carbonate,and hydrous clay, such that at least a portion of the hydrous clay is atleast partially calcined and the at least partially calcined clayadsorbs at least a portion of alkali present in the furnace.
 89. Amethod for operating a fluidized-bed reactor, the method comprising:introducing an alkali-containing material into a fluidized-bed reactor;introducing hydrous clay into the fluidized-bed reactor, the hydrousclay having a moisture content of at least about 5% by weight; heatingat least a portion of the alkali-containing material and hydrous clay,such that at least a portion of the hydrous clay is at least partiallycalcined and the at least partially calcined clay adsorbs at least aportion of alkali present in the fluidized-bed reactor; and removing atleast a portion of the at least partially calcined clay and adsorbedalkali from the fluidized-bed reactor.